Catalytic combustion systems are well known in gas turbine applications to reduce the creation of pollutants, such as NOx, in the combustion process. One catalytic combustion technique known as the rich catalytic, lean burn (RCL™) combustion process includes mixing fuel with a first portion of compressed air to form a rich fuel mixture. The rich fuel mixture is passed over a catalytic surface and partially oxidized, or combusted, by catalytic action. Activation of the catalytic surface is achieved when the temperature of the rich fuel mixture is elevated to a temperature at which the catalytic surface becomes active. Typically, compression raises the temperature of the air mixed with the fuel to form a rich fuel mixture having a temperature sufficiently high to activate the catalytic surface. After passing over the catalytic surface, the resulting partially oxidized rich fuel mixture is then mixed with a second portion of compressed air in a downstream combustion zone to produce a heated lean combustion mixture for completing the combustion process, typically by igniting and stabilizing the lean combustion mixture using a high temperature, NOx producing pilot flame. The heated combustion mixture form the first stage may reduce a size of a pilot flame required to stabilize combustion, but completion of combustion using a catalyst may eliminate the need to use a pilot flame. Catalytic combustion reactions may produce less NOx and other pollutants, such as carbon monoxide and hydrocarbons, than pollutants produced by homogenous combustion, even in the absence of a pilot flame.
In the past, catalysts have been used to partially combust rich fuel mixtures at temperatures up to about 800 degrees Centigrade (C.), but higher combustion temperatures have proven to be destructive to the catalysts and catalyst supports. Catalysts capable of operating at higher combustion temperatures of over 1000 degrees C. have been proposed, but such catalysts may have a catalytic activation temperature much higher than a compressed air temperature achievable by compression alone.